This invention relates to aqueous dispersions containing immiscible compounds for color imaging and products therefrom, and more particularly their use in laser-induced thermal transfer imaging.
Laser-induced thermal transfer processes are well-known in applications such as color proofing.
Laser-induced processes use a laserable assemblage comprising a donor element that contains a thermally imageable layer, the exposed areas of which are transferred to a temporary or a final receiver element by exposure to laser radiation which induces transfer of exposed areas of the thermally imageable layer from the donor element to the temporary or final receiver element. The (imagewise) exposure takes place only in a small, selected region of the laserable assemblage at one time, so that transfer of material from the donor element to the receiver element can be built up one pixel at a time. Computer control produces transfer with high resolution and at high speed.
In general, thermally imageable layers are designed so that additives and other ingredients are soluble in the coating solvent. Solubility considerations limit the range of additives and other ingredients that can be included in the coating solution. It is known to employ certain dispersants to disperse pigment particles, which are on the order of about 1 micron. However, dispersing immiscible compounds of larger size in thermally imageable, especially aqueous, coatings has not been described.
Infrared absorbing compounds are used in thermally imageable layers of donor elements. The IR absorbing compound acts as a light absorber. Exposure engines for thermal films using laser diodes, emitting in the 780 to 850 nm range, have become the standard in the industry and, therefore, a variety of IR absorbing compounds, with absorption spectra matching the emission of these laser diodes have also been synthesized. The preferred IR absorbing compounds have high absorbance at the wavelength of the incoming laser beam. Upon exposure, an IR absorbing compound absorbs the incoming radiation creating sufficient heat to transfer of the thermally imageable layer onto the receiver. However, the limited solubility of some IR absorbing compounds, especially in water, considerably limits the choice of IR absorbing compounds used in formulating donor elements.
The thermally imageable layer of the instant invention permits a broad range of immiscible compounds to be included in a thermally imageable layer without concern for this solubility. The invention overcomes the solubility problem by formulating a thermally imageable layer which comprises a dispersion of an immiscible compound. Thus, compatibility of the coating solvent with an immiscible compound is no longer a limiting factor for the choice of materials.
A thermally imageable layer which comprises a dispersed immiscible compound has been discovered which is suitable for use in thermal imaging without the problems associated with aqueous coating solutions containing certain immiscible compounds. Surprisingly, an aqueous dispersion has been discovered which is effective as a thermally imageable layer.
In one embodiment, the invention relates to a donor element comprising a thermally imageable layer comprising an aqueous dispersion comprising an immiscible compound and a polymeric dispersant, wherein the immiscible compound is a thermal amplification additive.
In another embodiment, the invention relates to a method of making a donor element comprising forming a dispersion of an immiscible compound and a polymeric dispersant, wherein the immiscible compound is a thermal amplification additive and applying the dispersion to a support.
In yet another embodiment, the invention relates to a method for making an image comprising:
(1) imagewise exposing to laser radiation a laserable assemblage comprising:
(A) a donor element comprising a thermally imageable layer prepared from an aqueous dispersion comprising an immiscible compound and a polymeric dispersant, wherein the immiscible compound is a thermal amplification additive; and
(B) a receiver element in contact with the thermally imageable layer of the donor element; the receiver element comprising:
(a) an image receiving layer; and
(b) a receiver support;
whereby the exposed areas of the thermally imageable layer are transferred to the receiver element to form an image on the image receiving layer;
(2) separating the donor element (A) from the receiver element (B), thereby revealing the image on the image receiving layer of the receiver element.
The so formed image may then be transferred to a permanent substrate by bringing the element formed in (2) in contact with the permanent substrate, followed by peeling away the receiver support.
In still another embodiment, the invention relates to a printed proof comprising:
an image receiving layer having an outer surface with a halftone dot thermal image applied thereto by imagewise exposure of a donor element comprising a thermally imageable layer comprising an aqueous dispersion comprising an immiscible compound and a polymeric dispersant, wherein the immiscible compound is a thermal amplification additive.
In still another embodiment, the invention relates to a method for making a color filter element on a substrate comprising thermally mass transferring a pigment colorant from a donor element to the substrate to form a pattern of at least one color on the substrate and then associating a liquid crystal display device with said pattern so that upon electronically addressing of liquid crystal within said liquid crystal display device at least a portion of the pattern of at least one color becomes visible, the donor element comprising a thermally imageable layer comprising an aqueous dispersion comprising the pigment colorant, an immiscible compound and a polymeric dispersant, wherein the immiscible compound is a thermal amplification additive.